configs: Fix Python 3 iterator and exec compatibility issues

Python 2.7 used to return lists for operations such as map and range,
this has changed in Python 3. To make the configs Python 3 compliant,
add explicit conversions from iterators to lists where needed, replace
xrange with range, and fix changes to exec syntax.

This change doesn't fix import paths since that might require us to
restructure the configs slightly.

Change-Id: Idcea8482b286779fc98b4e144ca8f54069c08024
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/16002
Reviewed-by: Gabe Black <gabeblack@google.com>

configs/ruby/Garnet_standalone.py

@@ -66,7 +66,7 @@ def create_system(options, full_system, system, dma_ports, bootmem,
     # controller constructors are called before the network constructor
     #
 
-    for i in xrange(options.num_cpus):
+    for i in range(options.num_cpus):
         #
         # First create the Ruby objects associated with this cpu
         # Only one cache exists for this protocol, so by default use the L1D